<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>void 0</title>
  </head>
  <body></body>
</html>
<script>
  var undefined = 100
  console.log(window.undefined) // undefined 只读

  function m() {
    var undefined = 100
    console.log(undefined)
  }
  m() // 100

  console.log(void 0) // undefined
</script>
